Cells in the prestriate cortex (area 18) of the rhesus monkey can be divided into six major classes on the basis of their physiologic responses to light stimuli. These classes are 1) color-selective, 2) direction-selective, 3) complex spot, 4) complex slit, 5) side-stopped, 6) inhibited by light. Cells in a given class respond differentially along a single stimulus dimension (i.e. color)and are typically unaffected by comparable changes along different stimulus dimensions (i.e. orientation, direction, etc.). These results suggest that the higher processing of visual information in the monkey involves parallel channels each specialized for the detection of a single feature of the visual environment at the expense of other features.